The present invention relates to reel-ups which operate on papermaking machines in general, and more particularly to force sensors which measure the nip loading between a reeling cylinder and a forming paper parent reel.
Paper which is made on a papermaking machine is wound up into reels which are periodically removed from the papermaking machine for further processing. The reels are large, sometimes 10 m in length and 3 or 4 m in diameter and weighing over 120 tons. To maintain the quality of the paper wound into the reel, the formation of the reel must be carefully controlled. There are three primary factors which control the quality of the reel formed, these are: the web tension, the center wind assist torque, and—most importantly—the nip loading between the paper reel and the reeling cylinder. The reeling cylinder is a roll drum which is normally driven and which is positioned just before the reel. The paper web typically wraps part of the reeling cylinder and then enters a nip formed between the reeling cylinder and a forming paper reel, and is wound onto the paper reel. It is the loading of this nip formed between the reeling cylinder and the paper reel which must be controlled to maximize the quality of the paper reel formed. The nip loading will typically be varied, typically decreasing in magnitude as the size of the paper reel increases.
The reel-up process begins with an empty spool or reel core which is brought down from a storage unit positioned above the reeling cylinder and into engagement with the reeling cylinder—typically on a pair of rotating arms which terminate in forks which extend on either side of the reel core bearings. The web is transferred from a fully formed paper reel to the empty spool or reel core in a process known as the reel change-over. Immediately, or once the paper reel has reached a given size, the roll spool is positioned between a pair of carriages which ride on level rails. The reel spool rotates freely on bearings contained within bearing housings. The bearing housings in turn are supported by the carriages which are movable on the horizontal rails. Web tension is controlled by the reeling cylinder, and torque is applied to the reel spool via center wind assist. Nip load is controlled by hydraulic cylinders which position the carriages on which the bearing housings and thus the paper reel are supported. The hydraulic cylinders adjust the position of the paper reel to control the nip loading of the paper reel with the reeling cylinder. Nip pressure may be monitored by monitoring the pressure in the hydraulic cylinders which position the carriages. More recently, load cells have been incorporated in the pins which join the hydraulic cylinders to the carriages. Although the use of load cells is superior to measuring hydraulic cylinder pressure, the use of load cells would benefit from more accurate determination of nip loading. What is needed is a load cell arrangement where load cells of smaller range and more accurate output can be used.